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Lowlevel-Coding / ComOS 0.1 Beta
« am: 27. July 2004, 15:54 »
PS: Mein Bootloader hab ich leider geklaut *schandeübermich*,
hab aber keinen anderen gefunden, der mit turbo c kerneln läuft:
hab aber keinen anderen gefunden, der mit turbo c kerneln läuft:
Code: [Auswählen]
[BITS 16]
[ORG 0x7C00]
START: JMP SHORT BEGIN
NOP ; not really needed, old school style
; +-------------------------------------------------------------+
; | Data section of boot.asm bootstrap file |
; +-------------------------------------------------------------+
bsOEM DB 'comosv01' ; OEM String
bsSectSize DW 512 ; Bytes per sector
bsClustSize DB 1 ; Sectors per cluster
bsRessect DW 1 ; # of reserved sectors
bsFatCnt DB 2 ; # of fat copies
bsRootSize DW 224 ; size of root directory
bsTotalSect DW 2880 ; total # of sectors if < 32 meg
bsMedia DB 0xF0 ; Media Descriptor
bsFatSize DW 9 ; Size of each FAT
bsTrackSect DW 18 ; Sectors per track
bsHeadCnt DW 2 ; number of read-write heads
bsHidenSect DD 0 ; number of hidden sectors
bsHugeSect DD 0 ; if bsTotalSect is 0 this value is
; the number of sectors
bsBootDrv DB 0 ; holds drive that the bs came from
bsReserv DB 0 ; not used for anything
bsBootSign DB 29h ; boot signature 29h
bsVolID DD 0 ; Disk volume ID also used for temp
; sector # / # sectors to load
bsVoLabel DB 'comos v 0.01' ; Volume Label
bsFSType DB 'FAT12 ' ; File System type
; +-------------------------------------------------------------+
; | Code section of boot.asm bootstrap file |
; +-------------------------------------------------------------+
BEGIN: CLI ; disable interrupts
MOV [bsBootDrv],DL ; save drive number
MOV AX,0x9000 ; put stack at 0x98000
MOV SS,AX
MOV SP,0x8000
MOV CX,[bsTrackSect] ; update int 1E FDC param table
MOV BX,0x0078
LDS SI,[DS:BX]
MOV BYTE [SI+4], CL
MOV BYTE [SI+9], 0x0F
MOV AX,CS
MOV DS,AX ; I know its not needed, but some
; BIOS fail if DS not set the hard
; way, my Cannon 450 does anyways =(
STI ; enable interrupts again
PUSH DS
MOV DL,[bsBootDrv] ; DL = drive we booted from
XOR AX,AX
INT 0x13 ; reset disk drive controller
POP DS
JC bootfail2 ; error resetting controller?
JMP _l1
bootfail2: JMP bootfail
_l1:
MOV AX,0x0000
MOV ES,AX ; correct segment registers
MOV DS,AX
MOV SI,bootmsg ; display load message
CALL putstr
; find the root directory on volume
XOR AX,AX
MOV AL,[bsFatCnt] ; number of FAT mirrors on disk
MOV BX,[bsFatSize] ; how many sectors a FAT uses
MUL BX ; AX returns FatCnt*FatSize
ADD AX,WORD [bsHidenSect] ; AX=AX+HiddenSectors
ADC AX,WORD [bsHidenSect+2] ; HidenSect is a double word, so...
ADD AX,WORD [bsRessect] ; AX now holds the sector where the
; VTOC (Volume Table Of Contents)
; starts
MOV WORD [BootSig],AX ; BootSig is used as temp to hold AX
CALL checkroot ; look into VTOC in root directory
; and see if we find our kernel image
XOR AX,AX
ADD AX,WORD [START] ; [START] = number of sectors in root
ADD AX,WORD [bsVolID] ; sector number where kernel image
; starts, but not correct value yet..
ADD AX,WORD [BootSig] ;
SUB AX,2 ; correction for a mis-calc
MOV CX,WORD [bsVolID+2] ; number of sectors
MOV BX,0x8000
MOV ES,BX ; get ready to read sectors into mem
nextsector: PUSH AX ; save registers
PUSH CX
PUSH DX
PUSH ES
XOR BX,BX ; set zero offset
CALL readsect ; read a sector
POP ES ; restore registers
POP DX
POP CX
POP AX
MOV BX,ES
ADD BX,0x20 ; increment address 512 bytes
MOV ES,BX
INC AX ; read next sector
LOOPNZ nextsector
MOV DX,0x3F2
XOR AL,AL
OUT DX,AL ; turn off floppy disk motor
MOV SI,bootgood
CALL putstr
MOV DL,[bsBootDrv] ; don't forget our bootdrive
MOV AX,0x8000 ; set segment registers and jump
MOV ES,AX
MOV DS,AX
PUSH AX
XOR AX,AX
PUSH AX
RETF
checkroot:
PUSH AX ; save registers
PUSH BX
PUSH CX
PUSH DX
PUSH SI
PUSH DI
MOV AX,0x8000 ; put root directory at 0x80000
MOV ES,AX
MOV AX,32 ; AX = ((32*RootSize)/512) + 2
MUL WORD [bsRootSize]
DIV WORD [bsSectSize]
MOV CX,AX ; cx holds # of sectors in root
MOV WORD [START],AX
MOV AX,WORD [BootSig] ; get prev. saved loc. for root dir
r1: XOR BX,BX
PUSH CX ; save count
PUSH AX ; save sector number
PUSH ES
PUSH DX
CALL readsect
XOR BX,BX
l_1: MOV DI,BX ; set address to check from
MOV CX,11 ; check 11 bytes
MOV SI,FileName ; address of string to check with
REPZ CMPSB
JE foundit ; we found our FileName in the VTOC
ADD BX,32 ; check next entry
CMP BX,[bsSectSize] ; end of sector?
JE l_2
JMP l_1
l_2: POP DX ; restore registers
POP ES
POP AX
POP CX
INC AX ; read next sector
LOOPNZ r1
JMP bootfail
foundit: POP DX ; get these off the stack
POP ES
POP AX
POP CX
MOV DI,0x1A ; get clustor #
ADD DI,BX
PUSH BX ; save bx for finding # of sectors
MOV AX,[ES:DI]
XOR BX,BX ; calculate sector #
MOV BL,[bsClustSize]
MUL BX ; ax holds sector #
MOV WORD [bsVolID],AX
POP BX ; get location of directory entry
MOV DI,0x1C
ADD DI,BX
MOV AX,[ES:DI] ; put number of bytes in ax
XOR DX,DX
MOV BX,[bsClustSize] ; # of bytes / 512
DIV BX
INC AX
MOV WORD [bsVolID+2],AX ; save number of sectors to load
POP DI ; restore registers
POP SI
POP DX
POP CX
POP BX
POP AX
RET ; return to caller
; +-------------------------------------------------------------+
; | Routines used over and over in boot.asm below... |
; +-------------------------------------------------------------+
putstr: ; SI = address of string to display
LODSB
OR AL,AL
JZ SHORT putstrd
MOV AH,0x0E
MOV BX,0x0007
INT 0x10 ; print character to CRT
JMP putstr
putstrd: RETN ; return to caller
bootfail: ; display failure message
MOV SI,bootbad ; display error message
CALL putstr
XOR AX,AX ; wait for keypress
INT 0x16
JMP 0xFFFF:0000 ; reboot machine
readsect: ; ES:BX = Location ; AX = Sector
MOV SI,[bsTrackSect]
DIV SI ; divide logical sect by track size
INC DL ; sector # begins at 1
MOV [bsReserv],DL ; sector to read
XOR DX,DX ; logical track left in ax
DIV WORD [bsHeadCnt] ; leaves head in dl, cyl in ax
MOV DH, [bsBootDrv] ;
XCHG DL,DH ; head to dh, drive to dl
MOV CX,AX ; cyl to cx
XCHG CL,CH ; low 8 bits of cyl to ch, hi 2 bits
SHL CL,6 ; shifted to bits 6 and 7
OR CL, BYTE [bsReserv] ; or with sector number
MOV AL,1 ; number of sectors
MOV AH,2 ; use read function of int 0x13
PUSH DS
INT 0x13 ; read sector
POP DS
JC bootfail ; display error message
RET ; return to caller
; +-------------------------------------------------------------+
; | Some more data used within boot.asm bootstrap file |
; +-------------------------------------------------------------+
bootmsg DB 'Starting ComOS ver 1 . . .',13,10,13,10,'BOOT STATUS: ',0
bootgood DB 'GOOD',13,10,0
bootbad DB 'BAD',13,10,0
FileName DB 'KERNEL BIN'
times 512-($-$$)-2 db 0
BootSig DB 0x55, 0xAA
Scorpion
